Nylon yarns and products made therefrom, such as fabrics and carpeting, have long been colored by treatment with acid, cationic, or other types of dyes. Recently, yarn producers have begun incorporating colored pigments into nylon yarns to improve their resistance to degrading and fading in ultraviolet light, to provide improved resistance to chemicals and noxious fumes, and to provide permanent coloration which is not removed by washing. While some pigments can be mixed easily into the nylon without adversely affecting the filament spinning operation, most pigments--and particularly organics--cause some difficulties while being mixed into the nylon or in subsequent melt-spinning and drawing operations. In general, organic pigments cross-link nylon, change its viscosity, increase the rate of crystallization and spherulite formation resulting in increased draw tension, weakened fibers, and more filament breaks.
European Patent Publication No. 0373655 ("Anton et al."), published Jun. 20, 1990, discloses processes for making stain-resistant, pigmented-colored polyamide fibers with acceptable levels of spinning performance. Those processes involve forming a random nylon copolymer made with up to 4.0 weight percent of a cationic dye additive such as 5-sulfoisophthalic acid or its salts, adding a pigment dispersed in a matrix of nylon 6 and a nylon 6,6/6,10/6 multipolymer to the random copolymer, and melt-spinning the pigment/polymer blend.
The pigment dispersions used in making such fibers are typically prepared by first combining the raw pigment with the nylon multipolymer in roughly equal percentages by weight, melting and resolidifying the combination to form pigmented pellets of the multipolymer. These pellets are then remelted or "let-down" in an equal or greater amount of nylon 6, mixed thoroughly to form a uniform dispersion, resolidified, and pelletized. Certain pigments, however, remain very difficult to spin and draw when dispersed in such matrices.
Ways of reducing the impact of such pigments on nylon spinning and drawing performance would permit the use of a wider selection of colored pigments, both organic and inorganic, and would enable fiber producers to offer a complete range of styling colors without encountering serious product deficiencies or operating difficulties.